Coloured composition with increased stress cracking resistance

ABSTRACT

The invention relates to a composition containing, in relation to the total weight of said composition, A) between 50.0% by weight and 99.5% by weight of at least one (meth)acrylate (co)polymer and B) between 0.5% by weight and 50.0% by weight of at least one copolymer, obtained by the polymerisation of a monomer mixture consisting of i. between 70% by weight and 92% by weight of a vinyl aromatic monomer and ii. between 8% by weight and 30% by weight of acryl nitrile or methacryl nitrile or mixtures thereof iii. between 0% by weight and 22% by weight of at least one other monomer, the composition having at 50° C. a ΔE of less than 0.15, ΔE being defined according to the relationship (1): (1) in which ΔL*: the modification of the colour co-ordinates L* compared with the colour co-ordinates L* at 23° C., Δa*: the modification of the colour co-ordinates a* compared with the colour co-ordinates a* at 23° C., Δb*: the modification of the colour co-ordinates b* compared to the colour co-ordinates b* at 23° C., and the composition contains at least one (meth)acrylate (co)polymer a) with a solution viscosity in chloroform at 25° C. (ISO 1628 part 6) greater than 55 ml/g. The moulded bodies that can be obtained from the composition are characterised in particular by improved stress cracking resistance and are suitable in particular for use in coatings, paints or films.

The present invention relates to a coloured composition having increasedstress cracking resistance and its use.

PRIOR ART

Polymethyl methacrylate (PMMA) compositions have long been used in theautomotive sector, in particular as rear light covers and instrumentcovers. In recent years, this material has also increasingly been usedfor shaped articles coloured so that they are opaque. Applications hereare, inter alia, spoilers, pillar claddings, window guide strips,exterior mirrors and exterior mirror bases.

These PMMA compositions are usually processed by extrusion, coextrusion,injection moulding or multicomponent injection moulding to givemouldings for the outdoor area. In these applications, at least theuppermost layer therefore consists of PMMA. Owing to the stability toweathering and surface hardness of PMMA, said layer protects thematrices underneath.

Since the mouldings are frequently provided with a dark colouring (thePMMA layer itself or the layers underneath), they are heated toconsiderable extent in sunlight. High heat distortion resistance istherefore a requirement with regard to the PMMA composition so that theappropriate climatic tests of the mouldings are passed and no softeningof the moulding occurs.

In addition, the mouldings must have high stress cracking resistance andhigh resistance to chemicals, since these applications often come intocontact with cleaning agents, petrol and other aggressive agents.

Furthermore, the known properties of PMMA compositions or PMMAmouldings, such as processability and mechanical properties, must beretained.

EP 0 508 173 B1 describes the use of polymer blends comprising 55% byweight to 98% by weight of PMMA, 2% by weight to 45% by weight of astyrene-acrylonitrile copolymer (SAN) and optionally further processingauxiliaries for the production of various shaped articles. According tothe description, the PMMA contains at least 80% by weight of methylmethacrylate (MMA) units. In the examples, formation of stress cracks isobserved after 2.1 min to 5.5 min. However, this value is not comparablewith the existing results according to the ESCR test. The Vicatsoftening temperature of an exemplary PMMA-SAN polymer blend is 106° C.

Similarly, EP 0 627 461 B1 discloses a weathering-resistant blendcomprising 49% by weight to 99% by weight of PMMA and 0.95% by weight to50% by weight of SAN and 0.05% by weight to 1% by weight of a certainstabilisation packet. Here too, PMMA contains at least 80% by weight ofMMA units. In the examples, formation of stress cracks is observed after680 s to 750 s. However, this value is not comparable with the existingresults according to the ESCR test. An improvement in the heatdistortion resistance is not described.

JP 03-217446 A2 relates to a blend of a copolymer of aromatic vinylmonomers and (meth)acrylic acids, PMMA and SAN. The blends havecomparatively high heat distortion resistance values (114° C.). However,the transmittance of the mouldings is only 84%.

JP 02-272050 A2 describes a blend having good heat distortion resistanceand impact strength, comprising

-   -   a) a copolymer of 40% by weight to 90% by weight of MMA, 5% by        weight to 20% by weight of maleic anhydride, 5% by weight to 40%        by weight of styrene and 1% by weight to 15% by weight of        C₁₋₄-alkyl acrylate,    -   b) a copolymer of acrylonitrile and aromatic vinyl compounds or        an MMA-C₁₋₄-alkyl acrylate copolymer,    -   c) an impact modifier comprising rubber grafted with        acrylonitrile and an aromatic vinyl compound.

The difference between the refractive index of the mixture of componentsa) and b) and that of component c) should be not more than 0.005.Nevertheless, such compositions have a strong dependency of the opticalproperties, in particular the transparency and/or the colour impression,on the temperature.

The application WO 2005/047392A1 discloses a polymer mixture whichcontains the following components:

-   -   a) a low molecular weight (meth)acrylate (co)polymer,        characterized by a solution viscosity in chloroform at 25° C.        (ISO 1628—part 6) of less than or equal to 55 ml/g,    -   b) an impact modifier based on crosslinked poly(meth)acrylates,    -   c) a higher molecular weight (meth)acrylate (co)polymer,        characterized by a solution viscosity in chloroform at 25° C.        (ISO 1628—part 6) of greater than or equal to 65 ml/g and/or    -   d) a further (meth)acrylate (co)polymer differing from a),        characterized by a solution viscosity in chloroform at 25° C.        (ISO 1628—part 6) of 50 to 55 ml/g,

it being possible for the components a), b), c) and/or d), each byitself, to be understood as meaning individual polymers or mixtures ofpolymers, a), b), c) and/or d) summing to 100% by weight,

it being possible for the polymer mixture also to contain customaryadditives, auxiliaries and/or fillers. On wetting of the surface withisopropanol, a test specimen produced from the polymer mixture shouldhave a fracture time greater than 1800 s at constant outer fibre strainof 0.39% and a fracture time greater than 700 s at constant outer fibrestrain of 0.50%. However, a strong dependency of the optical properties,in particular the transparency and/or the colour impression, on thetemperature is once again observable. Furthermore, in particularimproved stress cracking resistance and better processability aredesirable.

Object and Achievement

It was the object of the present invention to provide possibilities forimproving the stress cracking resistance of coloured compositions and ofmouldings. At the same time, as high a heat distortion resistance aspossible and as good optical properties as possible should be achieved.In particular, as small a temperature dependence of the visualappearance of the compositions and of the mouldings as possible wasdesired. Furthermore, mechanical properties which are as good aspossible, processability which is as good as possible and long-termstability and weathering resistance which are as high as possible shouldbe realised. It is also intended to indicate particularly expedientprocesses for the preparation of the novel compositions and mouldingsand particularly advantageous potential uses.

This and further objects which are inevitably derived from or directlyarise out of the above considerations are achieved by a colouredcomposition having all the features of the present claim 1. Thesubclaims relating back to this claim describe particularly expedientdevelopments of the composition, and the further claims relate toparticularly advantageous applications of the composition.

By providing a coloured composition which contains, based in each caseon its total weight,

-   -   A) 50.0% by weight to 99.5% by weight of at least one        (meth)acrylate (co)polymer and    -   B) 0.5% by weight to 50.0% by weight of at least one copolymer        obtainable by polymerisation of a monomer mixture comprising        -   i. 70% by weight to 92% by weight of a vinylaromatic monomer            and        -   ii. 8% by weight to 30% by weight of acrylonitrile or            methacrylonitrile or mixtures thereof and        -   iii. 0% by weight to 22% by weight of at least one further            monomer,

the composition having a ΔE of less than 0.15 at 50° C., ΔE being asdefined below, and the composition containing at least one(meth)acrylate (co)polymer a) having a solution viscosity in chloroformat 25° C. (ISO 1628—part 6) of greater than 55 ml/g, it is possible, ina manner which was not directly foreseeable, to provide a colouredcomposition which is outstandingly suitable for the production ofmouldings having improved stress cracking resistance. The compositioncan be prepared and processed in a comparatively simple manner, inparticular with relatively little energy consumption, and also permitsthe realisation of demanding part geometries.

At the same time, the articles which can be produced from thecomposition are distinguished by a combination of advantageousproperties:

-   -   They have very good optical properties, in particular high        colour constancy, and show comparatively little dependence of        the optical appearance on the temperature.    -   They have very high heat distortion resistance.    -   They exhibit outstanding mechanical properties, in particular a        high modulus of elasticity and a comparatively high Vicat        softening temperature.    -   The long-term stability and weathering resistance of the        mouldings is likewise outstanding.

CARRYING OUT THE INVENTION

(Meth)acrylate (co)polymer A)

The invention relates to a moulding material which contains at least one(meth)acrylate (co)polymer A). The (meth)acrylate (co)polymer may bepresent both as individual polymer and as a mixture of a plurality ofpolymers.

Properties of the (meth)acrylate (co)polymer A)

The (meth)acrylate (co)polymer or (co)polymers is or are preferablychosen in the proportions and in the composition so that a test specimenproduced from the (meth)acrylate (co)polymer or (co)polymerssimultaneously has the following properties:

-   -   I. a tensile modulus (ISO 527) of at least 2600 MPa, preferably        at least 2750 MPa, particularly preferably at least 2850 MPa, in        particular at least 3000 MPa,    -   II. a Vicat softening temperature VST (ISO 306-B50) of at least        109° C., preferably at least 110° C., particularly preferably at        least 112° C., in particular in the range from 110° C. to 125°        C.,    -   III. a tensile strength (ISO 179-2D, flatwise) of at least 17        kJ/m², preferably at least 18 kJ/m², preferably at least 20        kJ/m², particularly preferably at least 25 kJ/m², in particular        at least 30 kJ/m²,    -   IV. a melt volume flow rate MVR (ISO 1133, 230° C./3.8 kg) of at        least 1.5 cm³/10 min, preferably at least 1.65 cm³/10 min,        particularly preferably at least 2.0 cm³/10 min, in particular        at least 3.0 cm³/10 min.

Customary additives, auxiliaries and/or fillers are expediently chosenso that the above mentioned property profile is as far as possible notadversely affected or is at most slightly adversely affected.

Further Properties

Furthermore, the (meth)acrylate (co)polymer or (co)polymers is or arepreferably present in the proportions and in the composition such that atest specimen produced from the (meth)acrylate (co)polymer or(co)polymers also has at least some of the following properties:

Intrinsic Colour

-   -   Light transmittance T_(D65) according to DIN 5033/7 of at least        50%, preferably at least 55%.

Yellowness Index

-   -   The yellowness index, determinable according to DIN 6167        (illuminant D65, 10° on 3 mm layer thickness), should preferably        be less than 20, preferably less than 17.

Stress Cracking Resistance (ESCR Method)

-   -   Fracture time on wetting of the surface with isopropanol and        with constant outer fibre strain of        -   0.39%:>1800 s        -   0.50%:>700 s

Surface Gloss

-   -   R(60°):>48%, preferably >50%

According to the invention, the composition is distinguished, interalia, in that it contains at least one (meth)acrylate (co)polymer a)having a solution viscosity in chloroform at 25° C. (ISO 1628—part 6) ofgreater than 55 ml/g, preferably greater than or equal to 65 ml/g, inparticular in the range from 68 ml/g to 75 ml/g.

This may correspond to a molecular weight M_(w) (weight average) of160000 g/mol (determination of M_(w) by means of gel permeationchromatography using polymethyl methacrylate as a calibration standard).The determination of the molecular weight M_(w) can be effected, forexample, by gel permeation chromatography or by a light scatteringmethod (cf. H. F. Mark et al., Encyclopedia of Polymer Science andEngineering, 2nd. Edition, Vol. 10, page 1 et seq., J. Wiley, 1989).

In a first very particularly preferred variant of the present invention,the (meth)acrylate (co)polymer a) is a copolymer of methyl methacrylate,styrene and maleic anhydride.

Suitable proportions may be, for example:

50% by weight to 90% by weight, preferably 70% by weight to 80% byweight, of methyl methacrylate,

10% by weight to 20% by weight, preferably 12% by weight to 18% byweight, of styrene and

5% by weight to 15% by weight, preferably 8% by weight to 12% by weight,of maleic anhydride.

Corresponding copolymers can be obtained in a manner known per se byfree radical polymerisation. EP-A 264 590 describes, for example, aprocess for the preparation of a moulding material from a monomermixture comprising methyl methacrylate, vinylaromatic, maleic anhydrideand optionally a lower alkyl acrylate, in which the polymerisation iscarried out to a conversion of 50% in the presence or absence of anonpolymerisable organic solvent, and in which the polymerisation iscontinued from a conversion of at least 50% in the temperature rangefrom 75° C. to 150° C. in the presence of an organic solvent to aconversion of at least 80% and then the low molecular weight volatileconstituents are evaporated.

JP-A 60-147 417 describes a process for the preparation of apolymethacrylate moulding material having high heat distortionresistance, in which a monomer mixture comprising methyl methacrylate,maleic anhydride and at least one vinylaromatic is fed into apolymerisation reactor which is suitable for a solution or masspolymerisation, at a temperature of 100° C. to 180° C., and ispolymerised. DE-A 44 40 219 describes a further preparation process.

The proportion of the (meth)acrylate (co)polymer a), based on the totalweight of all (meth)acrylate (co)polymers, is preferably at least 75% byweight, preferably at least 85% by weight, particularly at least 95% byweight.

In a second very particularly preferred variant of the presentinvention, the (meth)acrylate (co)polymer a) is a homopolymer orcopolymer of 80% by weight to 100% by weight, particularly preferably of90% by weight-99.5% by weight, of methyl methacrylate units polymerisedby a free radical method and optionally of 0% by weight-20% by weight,preferably of 0.5% by weight-10% by weight, of further comonomers whichcan be polymerised by a free radical method, e.g. C₁- to C₄-alkyl(meth)acrylates, in particular methyl acrylate, ethyl acrylate or butylacrylate.

Particularly preferred copolymers are those comprising 95% by weight to99.5% by weight of methyl methacrylate and 0.5% by weight to 5% byweight, preferably 1% by weight to 4% by weight, of methyl acrylate.

Expediently, the composition furthermore contains at least one lowmolecular weight (meth)acrylate (co)polymer b) having a solutionviscosity in chloroform at 25° C. (ISO 1628—part 6) of less than orequal to 55 ml/g, preferably less than or equal to 50 ml/g, inparticular 45 ml/g to 55 ml/g.

This may correspond to a molecular weight M_(w) (weight average) of95000 g/mol (determination of M_(w) by means of gel permeationchromatography using polymethyl methacrylate as a calibration standard).The determination of the molecular weight M_(w) can be effected, forexample, by gel permeation chromatography or by a light scatteringmethod (cf. H. F. Mark et al., Encyclopedia of Polymer Science andEngineering, 2nd. Edition, Vol. 10, page 1 et seq., J. Wiley, 1989).

The (meth)acrylate (co)polymer b) is preferably a copolymer of methylmethacrylate, styrene and maleic anhydride.

Suitable proportions may be, for example:

50% by weight to 90% by weight, preferably 70% by weight to 80% byweight, of methyl methacrylate,

10% by weight to 20% by weight, preferably 12% by weight to 18% byweight, of styrene and

5% by weight to 15% by weight, preferably 8% by weight to 12% by weight,of maleic anhydride.

Valuable information on the preparation of such copolymers can beobtained, inter alia, from EP-A 264 590, JP-A 60-147 417 and DE-A 44 40219.

The (meth)acrylate (co)polymer b) can be prepared, for example, byadding 1.9 g of tert-butyl perneodecanoate and 0.85 g oftert-butylperoxy-3,5,5-trimethylhexanoate as a polymerisation initiatorand 19.6 g of 2-mercaptoethanol as a molecular weight regulator and 4.3g of palmitic acid to a monomer mixture comprising, for example, 6355 gof methyl methacrylate, 1271 g of styrene and 847 g of maleic anhydride.The resulting mixture can be introduced into a polymerisation chamberand degassed, for example for 10 minutes. Thereafter, polymerisation canbe effected in a water bath, for example for 6 hours at 60° C. and thenfor 30 hours at a water bath temperature of 55° C. After about 30 hours,the polymerisation mixture reaches its maximum temperature of about 126°C. After removal of the polymerisation chamber from the water bath, thepolymer is thermostated appropriately in the polymerisation chamber forabout a further 7 hours, for example at 117° C. in the air in an oven.

The (meth)acrylate (co)polymers a) and b) are advantageously present inthe following ratios which preferably sum to at least 75% by weight,preferably to at least 90% by weight, in particular to 100% by weight,based on the total weight of all of the (meth)acrylate (co)polymers.

(Meth)acrylate (co)polymer a): 25% by weight to 75% by weight,preferably 40% by weight to 60% by weight, in particular 45% by weightto 55% by weight, (Meth)acrylate (co)polymer b): 25% by weight to 75% byweight, preferably 40% by weight to 60% by weight, in particular 45% byweight to 55% by weight.

Copolymer B)

In addition to the (meth)acrylate (co)polymer, the moulding materialaccording to the invention contains at least one further copolymer (SANcopolymer) B) which is obtainable by polymerisation of a monomer mixturecomprising

-   -   i. 70% by weight to 92% by weight, preferably 75% by weight to        82% by weight, in particular 78% by weight to 81% by weight, of        at least one vinylaromatic monomer and    -   ii. 8% by weight to 30% by weight, preferably 18% by weight to        25% by weight, in particular 19% by weight to 22% by weight, of        acrylonitrile or methacrylonitrile or mixtures thereof,    -   iii. 0% by weight to 22% by weight of at least one further        monomer.

Particularly suitable vinylaromatic monomers are styrene,α-methylstyrene, tert-butylstyrene, monochlorostyrene and vinyltoluene,particularly preferably styrene and α-methylstyrene.

Furthermore, SAN copolymers having a molecular weight (weight averageM_(w)) of 60 000 g/mol to 300 000 g/mol, preferably of 100 000 g/mol to200 000 g/mol, which were preferably prepared by the process describedin British Patent 14 72 195, have proved to be very particularly useful.The molecular weight is determined in a manner known per se, inparticular by light scattering methods.

The amount of component B), based on the total weight of the mouldingmaterial, is, according to the invention, 0.5% by weight to 50.0% byweight, preferably 20.0% by weight to 40.0% by weight.

The amounts of components A) and B) preferably sum to at least 75% byweight, preferably to at least 90% by weight, in particular to 100% byweight, based on the total weight of the composition.

The preparation of component B) is carried out as a rule by knownpolymerisation processes, such as mass, solution, emulsion or beadpolymerisation. Such processes are described, for example, inKunststoffhandbuch [Plastics Handbook], editors Vieweg and Daumiller,volume V; Polystyrol [Polystyrene], Carl-Hanser-Verlag, Munich 1969,page 124 et seq., and in British Patent 14 72 195.

Customary Additives, Auxiliaries and/or Fillers

The composition according to the invention may also contain customaryadditives, auxiliaries and/or fillers, such as, for example, heatstabilisers, UV stabilisers, UV absorbers, antioxidants, provided thatthe properties of the composition according to the invention are notadversely affected by these additives.

UV Stabilisers and Free Radical Scavengers

Optionally present UV stabilisers are, for example, derivatives ofbenzophenone, the substituents of which, such as hydroxyl and/or alkoxygroups, are generally present in the 2- and/or 4-position. These include2-hydroxy-4-n-octyloxybenzophenone, 2,4-dihydroxybenzophenone,2,2′-dihydroxy-4-methoxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2-hydroxy-4-methoxybenzophenone. Furthermore, substituted benzotriazolesare very suitable as an added UV stabiliser and include in particular2-(2-hydroxy-5-methylphenyl)benzotriazole,2-[2-hydroxy-3,5-di(alpha,alpha-dimethylbenzyl)phenyl]benzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole,2-(2-hydroxy-3-5-butyl-5-methylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole,2-(2-hydroxy-5-tert-butylphenyl)benzotriazole,2-(2-hydroxy-3-sec-butyl-5-tert-butylphenyl)benzotriazole and2-(2-hydroxy-5-tert-octyl-phenyl)benzotriazole.

UV stabilisers which may furthermore be used are ethyl2-cyano-3,3-diphenyl-acrylate, 2-ethoxy-2′-ethyloxalic acid bisanilide,2-ethoxy-5-tert-butyl-2′-ethyloxalic acid bisanilide and substitutedphenyl benzoates.

The UV stabilisers may be present as low molecular weight compounds, asstated above, in the polymethacrylate materials to be stabilised.However, UV-absorbing groups in the matrix polymer molecules may also becovalently bonded after copolymerisation with polymerisable UV-absorbingcompounds, such as, for example, acrylic, methacrylic or allylderivatives of benzophenone derivatives or benzotriazole derivatives.

The proportion of UV stabilisers, it also being possible for this to bemixtures of chemically different UV stabilisers, is as a rule from 0.01%by weight to 1.0% by weight, especially from 0.01% by weight to 0.5% byweight, in particular from 0.02% by weight to 0.2% by weight, based onthe totality of all constituents of the polymethacrylate resin accordingto the invention.

Sterically hindered amines, which are known by the name HALS ((HinderedAmine Light Stabiliser) may be mentioned here as an example of freeradical scavengers/UV stabilisers. They can be used for inhibiting agingprocesses in finishes and plastics, especially in polyolefin plastics(Kunststoffe [Plastics], 74 (1984) 10, pages 620 to 623; Farbe+Lack[Paints+Finishes], 96^(th) year, 9/1990, pages 689 to 693). Thetetramethylpiperidine group present in the HALS compounds is responsiblefor the stabilising effect thereof. This class of compounds may beeither unsubstituted or substituted by alkyl or acyl groups on thepiperidine nitrogen. The sterically hindered amines do not absorb in theUV range. They trap free radicals formed, which once again the UVabsorbers are incapable of doing.

Examples of HALS compounds which have a stabilising effect and can alsobe used as mixtures are:

bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3-8-triazaspiro(4,5)decane-2,5-dione,bis(2,2,6,6-tetramethyl-4-piperidyl)succinate,poly(N-β-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidine succinicacid ester) and bis(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate.

The free radical scavengers/UV stabilisers are used in the compositionsaccording to the invention in amounts of 0.01% by weight to 1.5% byweight, especially in amounts of 0.02% by weight to 1.0% by weight, inparticular in amounts of 0.02% by weight to 0.5% by weight, based on thetotality of all constituents.

Lubricants or Mould Release Agents

In particular, lubricants or mould release agents which can reduce orcompletely prevent possible adhesion of the moulding material to theinjection mould are important for the injection moulding process.

Accordingly, lubricants, for example selected from the group consistingof the saturated fatty acids having less than C₂₀, preferably C₁₆ toC₁₈, carbon atoms or of the saturated fatty alcohols having less thanC₂₀, preferably C₁₆ to C₁₈, carbon atoms, may be present as auxiliaries.Small proportions of not more than 0.25% by weight, e.g. 0.05% by weightto 0.2% by weight based on the moulding material, are preferablypresent.

For example, stearic acid, palmitic acid and industrial mixtures ofstearic and palmitic acid are suitable. For example, n-hexadecanol,n-octadecanol and industrial mixtures of n-hexadecanol and n-octadecanolare furthermore suitable.

A particularly preferred lubricant or mould release agent is stearylalcohol.

Further Additives, Auxiliaries and/or Fillers

In the context of the present invention, the addition of the componentsc₁), c₂), c₃) and/or c₄) has also proved very particularly useful.

The component c₁) designates triaryl phosphites of the general formula(I)

in which R¹ and R² represent C₁-C₁₂-alkyl, such as methyl, ethyl,propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl,1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl,3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1-methylpentyl,2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl,1,3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl,2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl,1-ethyl-2-methylpropyl, n-heptyl, 1-methylhexyl, 2-methylhexyl,3-methylhexyl, 4-methylhexyl, 5-methylhexyl, 1-ethylpentyl,2-ethylpentyl, 1-propylbutyl, octyl, nonyl, decyl, undecyl and dodecyl,preferably C₃-C₁₂-alkyl radicals branched in 1-position (α), inparticular C₃-C₇-alkyl radicals, such as 1-methylethyl, 1-methylpropyl,1,1-dimethylethyl, 1-methylbutyl, 1,2-dimethylpropyl,1,1-dimethylpropyl, 1-ethylpropyl, 1-methylpentyl, 1,2-dimethylbutyl,1,3-dimethylbutyl, 1,1-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 1-ethyl-2-methylpropyl,1-methylhexyl, 1-ethylpentyl and 1-propylbutyl and1,1,3,3-tetramethylbutyl, 1,1,2,2,5,5-hexamethylhexyl, C₅-C₈-cycloalkyl,such as cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, preferablycyclohexyl,

C₆-C₁₀-aryl and C₆-C₁₀-aryl-C₁-C₄-alkyl, the aryl radicals of which maybe up to trisubstituted by C₁-C₄-alkyl, such as phenyl, naphthyl or2,2-dimethylbenzyl, and R³ denotes hydrogen and C₁-C₄-alkyl, such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl andtert-butyl, preferably hydrogen and methyl.

Examples of compounds (I) which are particularly important with regardto the present invention are the commercially availabletris(2,4-di-tert-butylphenyl)phosphite (Irgafos™ 168, Ciby-Geigy) andtris(nonylphenyl)phosphite, preferablytris(2,4-di-tert-butylphenyl)phosphite.

The component c₂) designates an amine of the general formula (II)

in which n represents the values 2 to 10, preferably 2 to 8. Compoundsof this type are also known by the designation HALS (hindered aminelight stabilisers) compounds and are commercially available.

An example of compounds (II) which are particularly important withregard to the present invention isbis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (commercially available bythe name Tinuvin™ 770 DF (Ciba Geigy)).

The component c₃) designates a benzotriazole of the general formula(III)

in which R⁴, R⁵ and R⁶ have the meaning of R¹.

Examples of compounds (III) which are particularly important with regardto the present invention are2-(2′-hydroxy-5′-methyl-phenyl)benzotriazole (commercially available bythe name Tinuvin™ P (Ciba Geigy)) or2-(2′-hydroxy-3′-dodecyl-5′-methyl-decyl)benzotriazole.

The component c₄) designates a phenol of the general formula (IV)

AB_(k)   (IV)

in which k denotes 1, 2 or 4 and, if k is 1, A represents —COOR⁷,—CONHR⁷,

R⁷ denoting C₁-C₂₁-alkyl and,

if k is 2, A representing —CONH—(CH₂)_(n)—CONH—,

in which p and m denote integers from 1 to 10 and, if k is 4, Arepresents

in which q denotes an integer from 1 to 4, and

B represents

in which R⁸ and R⁹ represent hydrogen, methyl or tert-butyl.

The addition of the component c₄) may in some cases lead to a furtherimprovement of the stress cracking resistance after weathering.

Examples of compounds (IV), which are particularly important with regardto the present invention, are octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (commercially availableby the name Irganox™ 1076 (Ciba Geigy)) and

The components c₁), c₂) and c₃) are preferably used as a mixture inorder to achieve a synergistic effect with regard to the improvement ofthe stress cracking resistance after weathering.

The preferred amounts of the components c₁) to c₃) are in each case inthe range from 1% by weight to 50% by weight, preferably from 30% byweight to 50% by weight, based on the sum of the amounts of thecomponents c₁) to c₃), the individual amounts summing to 100.

The amount of the component c₄) is preferably chosen in the range from0% by weight to 25% by weight, preferably in the range from 10% byweight to 25% by weight, based on the total amount of the components c₁)to c₃).

The total amount of the components c₁) to c₄), based on the total weightof the composition, is advantageously 0.05% by weight to 1% by weight,preferably 0.1% by weight to 0.5% by weight.

Colouring of the Composition

According to the invention, the composition is coloured. The colouringis preferably effected by colorants which may be dyes or pigments. Dyespreferably consist of dye molecules which substantially form a molecularsolution in the polymer matrix or are absorbed or chemically bonded inmore or less molecular form on the surface. Pigments on the other handcomprise in particular aggregates of dye molecules or minerals which areinsoluble in the polymer matrix.

A colorant may furthermore be insoluble in the polymer matrix at onetemperature and may behave like pigment. On the other hand, at another,generally higher, temperature, it may dissolve in the same polymermatrix as a dye. In the present invention, however, those colorantswhose solubility in the polymer matrix in the temperature range from 23°C. to 100° C. varies by at most 10%, based on the solubility at 23° C.,are particularly preferred.

Here, the colouring leads to at least one absorption in the visiblerange, i.e. at at least one wavelength in the range from 380 nm to 750nm. The absorption at 23° C. is preferably at least 1%, preferably atleast 5%, in particular at least 10%, compared with a sample of the samenature without colorant.

Here, the hue of the composition is described by the Lab colour system.It is standardized, has equal intervals, is apparatus-independent and isbased on human perception.

The colour space of the L*a*b* system is defined as follows:

-   -   L*=lightness (0=black, 100=white)    -   a*=red−green (−128=green, +127=red)    -   b*=yellow−blue (−128=blue, +127=yellow)

The composition according to the invention is distinguished by anexceptional colour constancy. Thus, it has a ΔE of less than 0.15,particularly preferably less than???, at 50° C., ΔE being definedaccording to the relationship (1):

ΔE=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}{square root over((ΔL*)²+(Δa*)²+(Δb*)²)}{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)},   (1)

in which

-   -   ΔL* designates the change in the colour coordinate L* compared        with the colour coordinate L* at 23° C.    -   Δa* designates the change in the colour coordinate a* compared        with the colour coordinate a* at 23° C.    -   Δb* designates the change in the colour coordinate b* compared        with the colour coordinate b* at 23° C.

At 80° C., ΔE is preferably less than 0.3, particularly preferably lessthan ???.

The addition of additives, such as, for example, impact modifiers,having substantially different thermal behaviour of the refractiveindices compared with the polymer matrix, should as far as possible beavoided since otherwise a significant temperature dependence of theoptical appearance is observable.

Melt Volume Flow Rate MVR of the Moulding Material

In the present invention, the composition preferably has a melt volumeflow rate MVR measured according to ISO 1133 at 230° C. and 3.8 kg, ofgreater than 1.2 cm³/10 min, preferably of greater than 1.5 cm³/10 min,in particular in the range from 1.7 cm³/10 min to 4.0 cm³/10 min.

Preparation of the Composition

The composition can be prepared by dry blending of the components, whichmay be present as powder, particles or preferably granules.

The composition can also be processed by melting and mixing theindividual components in the molten state or by melting dry premixes ofthe individual components to give a ready-to-use moulding material. Thiscan be effected, for example, in single-screw or twin-screw extruders.The extrudate obtained can then be granulated. Customary additives,auxiliaries and/or fillers can be directly admixed or added later by endusers as required.

Processing to Give Mouldings

The composition according to the invention is suitable as a startingmaterial for the production of mouldings having improved resistance tochemicals and stress cracking resistance. The forming of the compositioncan be effected by methods known per se, for example by processing viathe elastoviscous state, i.e. by kneading, rolling, calendering,extrusion or injection moulding, extrusion and injection moulding, inparticular injection moulding, being particularly preferred here.

The injection moulding of the composition can be effected in a mannerknown per se at temperatures in the range of 220° C.-260° C. (melttemperature) and a mould temperature of preferably 60° C. to 90° C.

The extrusion is preferably carried out at a temperature of 220° C. to260° C.

Mouldings

The mouldings obtainable in this manner are distinguished in that theyhave a ΔE of less than 0.15, particularly preferably less than 0.11, at50° C. and a ΔE of less than 0.3, particularly preferably less than 0.2,at 80° C.

The Vicat softening temperature of the mouldings according to ISO306-B50 is advantageously at least 109° C., preferably at least 112° C.

The nominal elongation at break of the mouldings according to ISO 527should preferably be at least 3.0%, particularly preferably 3.2%.

The modulus of elasticity of the mouldings according to ISO 527 isadvantageously greater than 3200 MPa, preferably 3500 MPa.

Furthermore, particularly suitable mouldings have a normalised stresscracking resistance factor greater than 0.80 in the stress crackingresistance test according to the ESCR method after 30 minutes at anouter fibre strain of 1%.

Uses

The mouldings according to the invention can be used in particular as acovering, finish or film. Injection mouldings can be used as parts ofhousehold appliances, communication devices, hobby or sports devices,bodywork parts or parts of bodywork parts in automotive, ship oraircraft construction. Typical examples of bodywork parts or parts ofbodywork parts of automobiles are, for example, spoilers, claddings,roof modules or exterior mirror housings.

EXAMPLES

The invention is explained in more detail below by examples, without itbeing intended to limit the concept of the invention thereby.

The following components a1), a2), b) and/or c) were used for thepolymer matrix.

The following was used as component a1): a commercially availablecopolymer of 75% by weight of methyl methacrylate, 15% by weight ofstyrene and 10% by weight of maleic anhydride, having a solutionviscosity number according to ISO 1628-6 at 25° C. in chloroform of 68ml/g.

The following was used as component (a2): a commercially availablecopolymer of 99% by weight of methyl methacrylate and 1% by weight ofmethyl acrylate, having a solution viscosity in chloroform at 25° C.(ISO 1628—part 6) of about 72 ml/g.

Preparation of Component b):

1.9 g of tert-butyl perneodecanoate and 0.85 g of tert-butylperoxy-3,5,5-trimethylhexanoate as a polymerisation initiator and 19.6 gof 2-mercaptoethanol as a molecular weight regulator and 4.3 g ofpalmitic acid are added to a monomer mixture comprising 6355 g of methylmethacrylate, 1271 g of styrene and 847 g of maleic anhydride.

The resulting mixture is introduced into a polymerisation chamber anddegassed for 10 minutes. Thereafter, polymerisation is effected in awater bath for 6 hours at 60° C. and then for 30 hours at a water bathtemperature of 55° C. After about 30 hours the polymerisation mixturereaches its maximum temperature of 126° C. After removal of thepolymerisation chamber from the water bath, the polymer is thermostatedin the polymerisation chamber for a further 7 hours at 117° C. in air inan oven.

The resulting copolymer is clear and virtually colourless and has a V.N.(solution viscosity number according to ISO 1628-6, 25° C., chloroform)of 48.7 ml/g. The flowability of the copolymer was determined accordingto ISO 1133 at 230° C. and 3.8 kg with MVR=3.27 cm³/10 min.

The component b) is thus a copolymer of 75% by weight of methylmethacrylate, 15% by weight of styrene and 10% by weight of maleicanhydride.

The following was used as component c): a commercially availablecopolymer of 99% by weight of methyl methacrylate and 1% by weight ofmethyl acrylate, having a solution viscosity in chloroform at 25° C.(ISO 1628—part 6) of about 53 ml/g.

®TYRIL 905UV from Dow Plastics was used as the SAN copolymer.

A dry blend was prepared from the individual components by means of atumbling mixer and was then compounded on a Leistritz LSM 30/34twin-screw extruder.

The compositions of the individual examples are documented in Table 1.

TABLE 1 Polymer matrix  ®TYRIL 905UV [% by weight] [% by weight] ExampleB1 Component a1) (70) 30 Comparative example VB1 Component a1) (100)Example B2 Component a2) (35) 30 Component b) (35) Comparative exampleVB2 Component b) (50) Component c) (50) Comparative example VB3Component b) (35) 30 Component c) (35)

The melt volume flow rate MVR (test standard ISO 1133: 1997) wasdetermined.

On an injection moulding machine Battenfeld BA 350 CD, tensile test barsand injection moulded discs were produced from all materials and testedwith regard to their properties by the following methods:

Vicat Determination of the Vicat softening temperature (16 h/80° C.):(test standard DIN ISO 306: August 1994) Modulus of Determination of themodulus of elasticity elasticity: (test standard: ISO 527-2) TensileDetermination of the elongation at break strength: (test standard: ISO527) ΔE: measured using 3 mm injection moulded sheets; measuringinstrument Color Eye 7000A, from Mac Beth; DIN 5033, DIN 6174 standards

Stress Crack Formation (ESCR):

Before the test, all samples were stored for at least 24 h at 23° C./50%relative humidity.

In the ESCR test according to Prof. Bledzki (A. Bledzki, C. Barth,Materialprüffung [Material Testing] 40, 10 (1998)), an outer fibrestrain which was constant as a function of time was applied by means ofa three-point bending arrangement. The test specimen (dimensions 80mm×20 mm×d, thickness d=4 mm) rested flat on two supports with a spacingL of 64 mm.

The specific experimental setup is illustrated in FIGS. 1 and 2. FIG. 1schematically shows the three-point bending arrangement in the ESCRtest. FIG. 2 shows an ESCR test apparatus (the arrangement from FIG. 1is upside down here). The cylindrical supports and the crossbeam have aradius of 10 mm.

The necessary sag s at a given outer fibre strain ε (in the middle ofthe test specimen on the side opposite the crossbeam) was calculated asin ISO 178 according to:

$\begin{matrix}{ɛ = \frac{6{sd}}{L^{2}}} & (2)\end{matrix}$

The sag s was adjusted by means of a knurled screw. ε was adjusted to avalue of 1%. After approaching the outer fibre strain (T₀), a hold timeof 2 min was allowed in order to await the first relaxation phenomena.At T=T₁=2 min, the filter paper already placed on top beforehand in themiddle and having the dimensions 50×10 mm² was wetted with the medium(isopropanol). The force which was required for maintaining the outerfibre strain was measured from T₁ as a function of time. The filterpaper was kept constantly moist with the medium in the course of themeasurement. The measurement was terminated on breaking of the testspecimen (force=0) but after 30 min at the latest.

This process was repeated for three test specimens. For comparison, theforce curve was also recorded for a test specimen which was exposed tothe same outer fibre strain but no medium. In the case of the sampleswithout influence of the medium, the measured force value decreasedslowly whilst the samples which are tested on the influence of themedium showed a faster decrease in force depending on resistance.

The time-dependent measure of the stress cracking resistance E_(T)^(norm) is obtained in this experiment from the ratio of the forcesrequired for maintaining the outer fibre strain F_(T) ^(mM) with andF_(T) ^(oM) without influence of the medium:

$\begin{matrix}{E_{T}^{norm} = \frac{F_{T}^{mM} \cdot F_{T\; 1}^{om}}{F_{T\; 1}^{mM} \cdot F_{T}^{oM}}} & (3)\end{matrix}$

Here, the forces are additionally based on their value at T₁ so that attime T₁: E_(T) ^(norm)=1. Three curves are a result in the diagram, foreach test specimen with influence of the medium. The reference in eachcase is the same measurement for the test specimen without the influenceof the medium. Normalised ESCR factors close to 1 characterize good ESCRresistance, and sharply decreasing values at E_(T) ^(norm) over time Tcharacterize poor resistance.

Results of the tests on the mixtures and the corresponding shapedarticles are shown in Table 2.

TABLE 2 B1 VB1 B2 VB2 VB3 Vicat 115.5 119 113.2 115 110.3 [° C.] MVR 1.91.9 2.9 4.5 5.2 [ml/10 min] ESCR No break - >40 No break - 0.08-0.422.6-3.9 [min] continuous continuous decrease decrease 0.92 at 0.85 at 30min 30 min Modulus of 3600 3702 3500 elasticity [MPa] Elongation 3.5 3.43.1 at break [%]

1. A coloured composition, comprising: based on the total weight of thecomposition, A) 50.0% by weight to 99.5% by weight of at least one(meth)acrylate (co)polymer and B) 0.5% by weight to 50.0% by weight ofat least one copolymer obtained by polymerisation of a monomer mixturecomprising: based on the total weight of B) i. 70% by weight to 92% byweight of a vinylaromatic monomer and ii. 8% by weight to 30% by weightof acrylonitrile, methacrylonitrile or a mixture thereof and iii. 0% byweight to 22% by weight of at least one further monomer, the sum of A)and B) being 100% by weight wherein the composition has a ΔE of lessthan 0.15 at 50° C., ΔE being defined by relationship (1):ΔE=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}{square root over((ΔL*)²+(Δa*)²+(Δb*)²)}{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)},   (1)in which ΔL* designates a change in the colour coordinate L* comparedwith the colour coordinate L* at 23° C. Δa* designates a change in thecolour coordinate a* compared with the colour coordinate a* at 23° C.Δb* designates a change in the colour coordinate b* compared with thecolour coordinate b* at 23° C., and the composition contains comprisesat least one (meth)acrylate (co)polymer a) having a solution viscosityin chloroform at 25° C. (ISO 1628—part 6) of greater than 55 ml/g. 2.The composition according to claim 1, wherein the (meth)acrylate(co)polymer a) has a solution viscosity in chloroform at 25° C. (ISO1628—part 6) of greater than or equal to 65 ml/g.
 3. The compositionaccording to claim 1, wherein the copolymer B) is obtained bypolymerisation of a monomer mixture comprising i. 75% by weight to 92%by weight of a vinylaromatic monomer and ii. 18% by weight to 25% byweight of acrylonitrile, methacrylonitrile or a mixture thereof.
 4. Thecomposition according to claim 1, wherein the (meth)acrylate (co)polymera) is a copolymer of methyl methacrylate, styrene and maleic anhydride.5. The composition according to claim 4, wherein the (meth)acrylate(co)polymer a) is a copolymer of 50% by weight to 90% by weight ofmethyl methacrylate, 10% by weight to 20% by weight of styrene and 5% byweight to 15% by weight of maleic anhydride.
 6. The compositionaccording to claim 4, wherein the composition comprises the(meth)acrylate (co)polymer a) in an amount of at least 75% by weight,based on the total weight of all (meth)acrylate (co)polymers.
 7. Thecomposition according to claim 1, wherein the (meth)acrylate (co)polymera) is a homopolymer or copolymer of at least 80% by weight of methylmethacrylate and optionally up to 20% by weight of further monomerscopolymerisable with methyl methacrylate.
 8. The composition accordingto claim 7, wherein the (meth)acrylate (co)polymer a) is a copolymer of95% by weight to 99.5% by weight of methyl methacrylate and 0.5% byweight to 5% by weight of methyl acrylate.
 9. The composition accordingto claim 7, the composition furthermore comprises at least one lowmolecular weight (meth)acrylate (co)polymer b) having a solutionviscosity in chloroform at 25° C. (ISO 1628—part 6) of less than orequal to 55 ml/g.
 10. The composition according to claim 9, wherein the(meth)acrylate (co)polymer b) is a copolymer of methyl methacrylate,styrene and maleic anhydride.
 11. The composition according to claim 10,wherein the (meth)acrylate (co)polymer b) is a copolymer of 50% byweight to 90% by weight of methyl methacrylate, 10% by weight to 20% byweight of styrene and 5% by weight to 15% by weight of maleic anhydride.12. The composition according to claim 9, wherein the (meth)acrylate(co)polymers a) and b) are present in the following ratios, based on thetotal weight of the (meth)acrylate (co)polymers: 25% by weight to 75% byweight of a) 25% by weight to 75% by weight of b).
 13. The compositionaccording to claim 1, wherein a lubricant is present as an auxiliary.14. The composition according to claim 13, wherein stearyl alcohol ispresent as a mould release agent.
 15. The composition according to claim1, wherein the composition has a melt volume flow rate MVR, measuredaccording to ISO 1133 at 230° C. and 3.8 kg, of greater than 1.2 cm³/10min.
 16. The composition according to claim 1, wherein the compositionis present in the form of granules.
 17. The composition according toclaim 1, wherein the composition has a ΔE of less than 0.3 at 80° C. 18.A process for producing a moulding, comprising forming a compositionaccording to claim
 1. 19. The process according to claim 18, comprisingextending or injection moulding the composition.
 20. A moulding producedby a process according to claim 18, wherein the moulding has a ΔE ofless than 0.15 at 50° C.
 21. The moulding according to claim 20, whereinthe moulding has a ΔE of less than 0.3 at 80° C.
 22. The mouldingaccording to claim 20, wherein the moulding has one or more followingproperties a. a Vicat softening temperature according to ISO 306-B50 ofat least 109° C., b. a nominal elongation at break according to ISO 527of at least 3.0% and c. a modulus of elasticity according to ISO 527 ofgreater than 3200 MPa.
 23. The moulding according to claim 20, whereinthe moulding has a normalised stress cracking resistance factor greaterthan 0.80 in the stress cracking resistance test according to the ESCRmethod after 30 minutes at an outer fibre strain of 1%.
 24. A filmcomprising the moulding according to claim
 20. 25. (canceled)